Hazards and Safety in Injection Molding

Table of Contents

  1. Introduction
  2. Principal Hazards
  3. Trauma/Hazard Control Mechanisms
  4. Standards
  5. Discussion and Conclusions
  6. References

I. Introduction

Industry

While the majority of manufacturing industries are in decline, plastic processors continue to grow at a rapid rate. Plastic processing is accomplished by one of four major processes: (1) injection molding, (2) blow molding, (3) extrusion or (4) rotational molding. Injection molding is the largest segment of the plastics market with approximately 5500 (down from 6000 in 1992) injection molding companies in North America. Although the statistics show a decline in the number of molders, this is due to a consolidation of the industry. The overall sales of the top 100 molders has risen by an average of 50% during the same time frame.

Injection molders manufacture a diverse array of products. Some of the most common segments of the industry are: (1) automotive, (2) major appliances, (3) household products or small appliances, (4) packaging (compact disc jewel boxes, food containers and cosmetics compacts), (5) business machines (computers, copiers), (6) telecommunications (cell phones, phones), (7) point of purchase displays & (8) outdoor products (lawn chairs, toys).

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Molding Machine Process and Modes

Injection molding machines are manufactured in two styles: vertical and horizontal. Although major differences exist in the construction and usage of these types of machines, the safety requirements are similar.

An injection molding machine is constructed in two pieces: (1) an injection unit and (2) a clamp unit. Both of these units are integral in the overall molding process. This process involves the melting of pelletized plastic in a plasticizing chamber (located in the injection unit) by a reciprocating screw. After melting, the reciprocating screw forces the "melt" into the mold under extreme pressures (generally in the 10,000 to 20,000 psi range). While the molten plastic hardens in the mold, forming the requisite product, the screw rotates in a reverse direction, melting more plastic and preparing for the next "shot." The reciprocating screw is actuated by hydraulic or electric means.

Another common activity involving the injection unit is a "purge." To purge the injection unit, the human moves the injection unit away from the mold and then causes the injection unit to extrude plastic onto the bed of the machine. Plastic degrades if heated for an extended time, thus purging becomes necessary.

During the injection cycle, the two halves of the mold must be clamped together tightly to withstand the high injection pressures. The amount of clamp force required varies depending on the size of the part, but this pressure ranges from 50 tons to 3000 tons and above. After the injection cycle has completed, and the plastic resolidified, then the clamp unit opens the two halves of the mold and ejects the products. The clamp unit is actuated either by a hydraulic cylinder that generates the forces or a "knuckle" approach for mechanical advantage.

An injection molding machine operates in three different modes. The first, full automatic, allows the machine to manufacture product with no human intervention. It simply melts plastic, shoots it into the mold and then ejects the product. During ejection, the product either falls onto a conveyor or chute, or the products are removed by robotic arms (typically for very cosmetic type products). This mode is generally used for production.

The second mode, semi-automatic, is used during the start up of the machine or for product that demands human intervention. In this mode, the machine operates automatically for one full cycle and then stops. The human must open the operator safety gate and then close it to actuate the next cycle. Insert molding, where a metal insert is placed into the mold prior to injection, is a case where human interaction is necessary. Another use of "semi" is for products that do not eject automatically.

The final mode, manual, is used exclusively for machine set up. In this mode, the machine takes no action without human involvement. The clamp will not close, injection unit not function nor will the ejection mechanism activate without the set up person instructing the machine to do so via a control panel. The purging procedure, detailed above, is a common use of manual mode.

As can be obviously seen, there are many opportunities for injuries to occur, as there are many energy sources involved.

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Uses of Auxiliary Equipment

The injection molding industry uses several auxiliary pieces of equipment. The first of these is the scrap grinder. Scrap grinders are used to chop up excess plastic or scrap parts. The plastic can then be reused for further production. These scrap grinders contain rotating blades that cut the plastic into small pellets.

A second piece of equipment common to this industry is the material dryer. Many plastics absorb water from the air (hygroscopic). To utilize this "wet" material, it must be placed into a dryer that removes this moisture. Otherwise, many quality defects become apparent. Dryers employ hot (approximately 180o F) air to remove the moisture.

A third auxiliary that causes safety issues are robots. Robots often remove the parts from the mold after the molding cycle and then place the parts onto a conveyor belt. The pieces can also be placed onto some type of automation, or other value added, activity.

The molds used in injection molding also cause hazardous conditions. These molds weigh in excess of 1000 pounds and must be placed into and taken out of the machines themselves.

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Specific Industry Issues

Appendix A contains the OSHA violations for SIC code 3089, Federal jurisdiction, from October 1996 until September 1997. During that period there were 340 organizations inspected with 2321 violations yielding a total penalty of $1,701,073.49. The violation that yielded the largest dollar volume of penalties was standard number 19040002 - Log and Summary of Occupational Injuries and Illnesses. The most frequent violation was from standard 19101200 - Hazard Communication, followed by standard 19100147 - The Control of Hazardous Energy, Lockout/Tagout.

Appendix B is the OSHA violations for SIC code 3089, North Carolina jurisdiction, from October 1996 until September 1997. 35 inspections occurred during this time period, with 419 violations yielding $77,350.45 in penalties levied. The largest dollar volume violation was due to standard 19100212 - Machines, General Requirements. The most frequent violation was from standard 19100305 - Electrical, Wiring Methods, Components & Equipment followed by standard 19100303 - Electrical Systems Design, General Requirements. Two of these inspections were due to accidents on the job (Fat Cat inspections), one of which was fatal.

The first accident that OSHA investigated involved the amputation of an arm. Per the accident investigation report (OSHA, 28 April 1997), the lower arm of a 20 year old male was lacerated by a "Shear Point Action." The report does not indicate what struck the arm. It does detail that the human factor failure was that the lockout/tagout procedure malfunctioned. Appendix C is the report published by OSHA for this investigation.

The second accident investigated was caused by a falling gantry that struck a 48 year old male in the chest. The bruises/contusions/abrasions that resulted were sufficient to be fatal. The environmental factor involved was an "overhead moving/ falling object" and the human factor, "insufficient/lack/written work practices & procedures" (OSHA, 18 July 1997). Appendix D contains the report of this incident. These two accidents were the first in 8 years for SIC code 3089 in North Carolina.

In 1989, a 40 year old male supervisor died as a result of being crushed by the clamp force of an injection molding machine. This person bypassed or removed the safety interlocks to work on the mold. Another person noticed that the machine was not in operation and proceeded to start the machine on an automatic cycle. As the machine cycled, it crushed the head of the supervisor using a "Pinch Point Action" (OSHA, 14 August 1989). For this accident, the company was issued violations for standard 95012901 - General Duty Clause and standard 19100212 - Machines, General Requirements. These violations cost the company $19,000.00 in fines and penalties.

Nationwide during 1996, SIC code 308 (miscellaneous plastic products, nec) caused 17 fatalities, 0.31% of the total number of private industry fatalities. 35.3% of these events were due to "contact with objects and equipment" (Bureau of Labor Statistics, 1996). The table did not include any of the other causes of fatalities.

The following two charts show BLS statistics from 1989 until 1996 (BLS, 1989-1996) on the number of nonfatal injuries and illnesses per 100 full time workers. SIC code 20 refers to manufacturing as a whole and SIC code 3089 is plastics products, nec.

The injury and illness rate (figure 1) shows that SIC code 3089 is decreasing at a faster rate than the overall manufacturing rate. Figure 2 shows that the injury rate is staying constant to the injury rate of SIC code 20.

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II. Principal Hazards

The principal hazards associated with injection molding machines include: (1) crushing injuries due to clamp mechanism, (2) burns due to hot plastic, (3) limb amputation due to clamp mechanism or plastic feeding mechanism, (4) slips, trips and falls due to loose plastic pellets on the floor and (5) electrocution due to failure to de-energize circuitry prior to maintenance operations. Other hazards exist in an injection molding company due to auxiliary equipment. These hazards include: (1) contusions and abrasions, (2) limb amputation due to scrap grinders, (3) being pinned by a robot or (4) burns from a hot mold.

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Injection Molding Machine

The clamp half of an injection molding machine contains many hazards. A common injury is the dismemberment, or death, of someone due to a mold closing on some part of the human body. In the first OSHA case referred to earlier (OSHA, 4/28/97) it could be speculated that the person's arm was caught between the mold halves and was then sheared off. In an interview with John Jarrells, he discussed how he severed the end of his middle finger on his left hand. He was working on a mold, when an operator inadvertently activated the machine, causing the mold to close on his hand (Jarrells). Finally, the third OSHA case (OSHA, 8/14/89) shows a fatality due to the mold being closed on a person's head.

Jarrells also discussed the issue of dismemberment due to a hand being caught in the "knuckle" part of the clamp mechanism. On older machines it is necessary to adjust the amount of stroke of the clamp by turning a nut on a screw mechanism contained in the clamp. It is easier to adjust this setting while the machine is energized. An energized machine allows the setup person to move the clamp forward and back to adjust the stroke. Jarrells told of a gentleman in his employ setting the stroke in this manner, when the clamp was activated prematurely. His hand caught in the screw mechanism and as the "knuckle" locked into position, it severed his hand from his arm.

On modern machines, the stroke is set by the action of a series of gears. These gears offer another source of hazardous energy. At Technimark, a setup person's shirt sleeve caught in the gear mechanism and the shirt was stripped off of his body. Fortunately, no injury occurred, but it is a simple logical jump to catching a hand or arm in the same gear mechanism.

The injection unit on a molding machine equals the clamp end for hazards, but, of a different nature. Since the injection unit melts plastic, the primary hazard is burns. Most plastics melt at a minimum of 400o F., well hot enough to cause severe burns. Typically, during an automatic cycle of the machine, the hot plastic cannot come in contact with a person. However, during the purging of the machine, the hot plastic is allowed to come out of the injection unit and fall onto the bed of the machine. During this purging, the plastic will sputter and splash. After purging, the hot plastic either remains on the bed of the machine or is placed on the floor of the plant until cool. It can then be safely discarded.

During an interview, Gary Bean related a story of a 22 year old female that was burned via a purging. She was standing nearby while the supervisor purged her machine and made it ready for production. After purging, the supervisor went to place the hot, melted plastic on the floor. As he turned to place it on the floor, carefully using a large screwdriver to maneuver the plastic, he inadvertently threw it on the arm of the operator. She suffered third degree burns on her arm as a result (Bean).

John Jarrells told of a person that lost the sight in one of their eyes due to hot plastic splashing on them. This person was setting the machine up for production, during which he purged the degraded plastic out of the barrel of the machine. As he was purging, the plastic sputtered and splashed. A nearby operator called out to the supervisor and as he turned to talk with the operator, the plastic splashed again. His eyeglasses did not have side shields on them and some of the hot plastic splashed into his eye, thus causing the loss of sight (Jarrells).

Burns can also occur due to the heat of the injection unit itself. To melt the plastic, the steel "barrel" of the injection unit must contain an equal portion of heat. A representative accident involving the barrel could be that a person has started to slip and reaches out for support. In place of holding the bed of the machine, they grab the barrel. A first or second degree burn would then ensue.

Electrocution can also occur due to contact with the barrel of the machine. The barrel is typically surrounded by heating elements that are electrically powered. Should one of these elements become ungrounded, shocks would be possible. This hazard is remote, but possible.

Another type of injury that occurs at the injection unit is finger dismemberment. The raw plastic pellets are fed from a hopper through a feed throat into the screw unit of the machine. The reciprocating screw pulls material into the injection unit of the machine. Occasionally, the feed throat does not allow proper flow, thus it must be cleaned out. The proper way to achieve this cleaning is to stop the machine and then clean the feed throat. However, this is obviously not the most economical way to clean. Supervisors, setup personnel and operators have been known to stick their fingers in the feed throat and attempt to push the plastic into the injection unit. The screw can then trap their fingers and lead to dismemberment.

Injection molding machines draw power from hydraulics and electricity. Contact with electrical circuits are another danger in dealing with these machines. Usually, supervisors, setup personnel and operators do not need to concern themselves with electrocution. This particular hazard falls to maintenance personnel during a repair operation. Electrocutions occur as a result of leaving the machine energized while attempting a repair. Many accounts detail experiences with electricity, ranging from simple "jolts" (110 volt power) to death from the 440 volt circuitry. The facility that contains the injection molding machines also offers the opportunity for electrocution. To power the plant, it is necessary to run "bus bars" of electrical power to all of the machines. These bus bars contain wiring that carries tremendous (up to 10,000 amperes) of current. Coming into contact with any of these bus bars could easily be lethal.

An example of electrocution comes from NIOSH (1987). A "set-up" man was killed while attending to a quality problem. As he closed the safety gate on the machine, he was also in contact with a grinder. The grinder had a ground fault and the machine provided a grounding route via the man. Thus, the 270 volts powering the grinder went through the body of the man, stopping his heart. No one at the company knew cardiopulmonary resuscitation and help was 16 minutes away.

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Slips, Trips and Falls

Slips, trips and falls occur in many ways within injection molding companies. The most common slip transpires because of plastic pellets on the floor. Plastic is transported to molders as pellets contained in bags, boxes, truck load or rail car. In truck load and rail car quantities, the pellets are stored in large, grain-style silos. The plastic enters the plant via pipes directly connected to the molding machines, thus preventing most spills. But, for companies that use bags or boxes, spills are common. With these pellets on the floor, it is nearly impossible to prevent slips. Fortunately, most of these slips are minor.

Falls can be much more dangerous. Prior to entering the injection unit of the molding machine, the pellets are stored in large hoppers attached to the top side of the injection unit. A vacuum system moves the plastic from box or silo to the hopper. This vacuum system contains a piece of equipment (the loader) that sits on top of the hopper. It is often necessary to construct platforms for personnel to attend to these loaders. These platforms require ladders and can be as high as 20 feet in the air. Falls transpire when a person attempts to maneuver the loader while either on the ladder or the platform.

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Auxiliary Equipment

The auxiliary equipment around an injection molding machine contain several hazards. The first piece of necessary auxiliary equipment is the mold itself. A mold consists of a minimum of approximately 1000 pounds of steel and assorted other metals. This chunk of metal must be positioned in the molding machine. Positioning the mold involves lifting it up and over the framework of the machine. This is done either by overhead cranes or by fork trucks with chains. Either of these methods have some inherent dangers of their own. Should the mold be mishandled, it can lead to crushed and/or severed limbs.

Molds also present a burn danger. To pragmatically mold product, the mold itself is often heated to a maximum of about 180o F. For efficient changeovers of the machine, the mold is pre-heated to the molding temperature. During the handling of the mold, the mold setter must be careful to not come in contact with the heated surfaces.

Scrap grinders present dismemberment perils to operators and setup personnel. The rotating blades contained in these machines can either directly amputate a body part, or it can trap loose clothing or jewelry. Glenn Looper recounts a story of a maintenance person that got a finger cut off by one of the blades. While sharpening the blades of a grinder, his hand slipped and he severed his finger. Fortunately, he was hustled to a hospital where they were able to reattach the finger (Looper).

Since grinders granulate material, it is possible for some of it to fly into the eye of a person operating the grinder. Gary Bean related an account of one such accident during his interview. The person was operating a grinder, granulating off quality pieces. As the machine chewed up the pieces, small, ground fragments of plastic flew into the air. Several of the bits of plastic ended up in the operator's eye. It took several minutes at an eyewash station to remove the plastic (Bean).

Dryers offer burn hazards to all personnel that work around molding machines. The dryer is connected to the material hoppers via hoses that carry the hot air to the material to eliminate the moisture. As these hoses are generally insulated, the danger is not great. Looper relates an account of a person that slipped and fell on some loose pellets on the floor. As they fell their hand and arm became entangled with the dryer hose. After sorting himself out and getting up, the only true harm was to his pride. No burn had occurred due to the dryer hose (Looper).

Machine mounted robots contain the second most prevalent source of hazards in injection molding companies. The major concerns with machine mounted robots are: (1) trapping, (2) falls and (3) electrocution. An example of trapping was related by Gary Bean during his interview:

A maintenance employee was in the process of setting up a manufacturing work cell. This involved installing two molds into two molding machines, after which the automation equipment was put into place. The final step was to assure that the robot would pick the parts out of the mold and then place them correctly onto the conveyor system of the automation. The mold and automation installations went according to plan. When the maintenance employee cycled the robots, he was standing too close to the conveying system. As the robot descended to drop the parts, it trapped the man by pinching his head between the robot arm and the conveying system. As the robot would not ascend until reaching its full downward position, the man's head prevented this, the man was trapped until power could be cut from the robot. This was to be accomplished by hitting an emergency stop button. The man could not reach the button to kill the power. Finally, the man was unable to scream out, as the robot had him pinned from the top of his head and his chin rested on the conveyor. Fortunately, a person saw the condition and cut the power switch off. The maintenance man suffered some bruising and a laceration on his head that required 8 stitches to close (Bean interview).

The second type of injury resulting from robots are falls. The robots are mounted on top of the injection molding machine. Most molding machines are approximately 9 feet high where the robot is mounted. To effectively work on the robot, it is necessary to use ladders and/or to climb on the molding machine or robot to reach the work area. The final type of injury suffered from robots is electrocution. This hazard is very similar to the electrocution hazard associated with the molding machine itself. However, the robots do not offer as serious a hazard as the molding machine. Robots typically only use 110 volt power, thus reducing the risk of a dangerous electrical incident.

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III. Trauma / Hazard Control Mechanisms

Injection Molding Machine

To overcome the hazards involved with the injection molding machine, the industry has voluntarily committed to several standards (ANSI 1990; SPI 1992; SPI 1996) that control the safety guidelines for the machines. Although the three standards apply to slightly different types of molding machines, the strategies for controlling each of the hazards are very similar.

The first hazard discussed earlier refers to the ability of the clamp unit to either dismember or kill. Mechanical guarding is an effective means of preventing these injuries. All three of the standards require that the clamp unit have fixed guards surrounding the "rearward" half of the clamp (ANSI 1990; SPI 1992; SPI 1996). These fixed guards prevent two types of clamp related injuries: (1) getting pinched/caught by the "knuckle" part of a clamp and (2) being caught by the gear that sets the amount of stroke for the machine. These fixed guards should also contain electric interlocks to avoid their being removed and the machine actuated.

The front half of the clamp unit calls for moveable guards (ANSI 1990; SPI 1992; SPI 1996) on the front and back of the machine. Placing molds and retrieving product from within the mold necessitates the ability open a guard. Also, during setup or due to quality issues, it is necessary to adjust the process of the machine. The ability to retrieve parts from within the mold is critical during processing. To protect the operator and all other personnel, a safety door is installed. The safety door blends three separate systems to prevent the mold from closing on a person.

The first system used is an electrical interlock. When the door is open, the electrical power circuit for the machine opens and will not allow power for closing the clamp. Oftentimes, the machine will have more than one electrical switch attached to the safety door.

The second system is a hydraulic interlock. As the clamp moves via hydraulic power, this interlock prevents the flow of hydraulic fluid into the mechanical cylinders that actuate the clamp unit.

The final system is a mechanical device that physically prevents the mold/clamp from closing. The device can either be a drop bar that actually blocks the mold from closing or a system of pawls and ratchets that engage to prevent movement. These physical devices differ on each model of machine, as the size and strength necessary changes. These devices must also be adjusted for each of the molds placed within the machine, particularly as the stroke of the clamp unit changes.

The back side of the clamp unit also has two separate guard systems. The rearward half again has fixed guards. The front half has a semi-fixed gate. This gate is only used for installation of molds, not for part removal. The back gate protects via an electric interlock (similar to front gate) and a hydraulic interlock (also similar to the front gate). It does not, however, have the mechanical device.

These systems "should be inspected at each eight hour shift to ensure proper operation (NSC Data Sheet I-454, 1988)." The stroke of the unit can sometimes "slip." Also, it is possible for the switches to become loose and less effective.

On low profile machines, a top fixed guard should also be installed. This prevents a person from reaching in from the top of the clamp unit and getting injured via this route. The majority of molding machines do not require this guard, as they are approximately 9 feet tall. Like the other fixed guards on the rearward half of the clamp, this guard, if installed, should have an electric interlock to prevent its being removed (NSC Data Sheet I-454, 1988).

The injection unit can also be controlled via guards. All three of the standards (ANSI 1990; SPI 1992; SPI 1996) again call for guards to protect the front, rear and top of the purging area. An electrical interlock insures that the guard is in place during the automatic running of the machine or during the purging cycle. Should viewing of the purge area be necessary, a window should be provided that will with stand the splashing of the plastic material without failure.

As an added precaution, safety glasses, with side shields, or face shields should be worn to avoid injury due to splashing of the hot plastic into a person's eyes. The standards (ANSI 1990; SPI 1992; SPI 1996) require that the company provide these personal protective equipment items to all employees.

Physical guards and heat blankets prevent injury due to burns. The blankets absorb the heat from the barrel of the machine, thus not allowing the transfer to a human that contacts the barrel. These blankets are not standard on any model of injection molding machine. They are offered as add-ons or after market products. The physical guards prevent contact with the electrical connections on the barrel, thus limiting the danger of electric shock.

Another hazard presented by the injection unit is that of finger dismemberment. To avoid this type of injury, guards are placed on the feed throat. The guards should adequately prevent a person from placing their fingers into the feed mechanism of the machine. This guard should also have an electric interlock that interrupts the machine cycle if the guard is removed. If guards are not feasible due to operating requirements, then warning signs should be placed in the feet throat area.

To prevent electrocution hazards, the company should establish an adequate lockout/tagout procedure. The company should also provide the means for positive lockout. For example, the company provides individual locks to all employees. This policy should be enforced vigorously, with discipline when necessary. Molding machines (and auxiliary equipment also) should be readily equipped with adequate lockout allowances. For example, holes should be put in the main power switches for the machine so that a lock can easily be mounted when the switch is in the off position. Another example would be to put holes in the contacts of the electric cords for auxiliary equipment, again allowing ease of insertion of locks.

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Slips, Trips and Falls

Slips, trips and falls are extremely difficult to prevent. To prevent slips and trips, a capable housekeeping system should be enforced. The policy should allow for sweeping of the area surrounding the molding machines frequently. This will avoid many slips be keeping the plastic pellets off of the floor. If possible, the company should also receive the pellets into a silo and pipe them into the hoppers of the machines. This helps to avert the possibility of pellets ending up on the floor.

Falls can be avoided. To eliminate the need to climb to an excessive height to clean up the vacuum system, a company can install a system that is not mounted on the machine. Modern material handling techniques allow for the hoppers to be mounted in the floor of the plant, thus making the heavy loaders available at waist level. On the machine itself is a simple, small hopper that contains only about 1 pound of material. This mini-hopper is much lower to the ground, again averting the necessity of climbing a ladder.

To sidestep the falls associated with machine mounted robots, a company should provide a safe aerial basket. The aerial basket would then be maneuvered over the machine, near the robot and allow the maintenance, or setup, person to perform operations on the robot.

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Auxiliary Equipment

Molds should be handled with extreme precision and care. Injection molding companies should provide overhead cranes to maneuver the molds. This methodology is safer than using fork trucks for mold handling. The cranes should be tested on a periodic basis to assure that they can still withstand the forces required. Also, since a chain is commonly used to connect the mold to the lift mechanism, the chain should be certified to withstand the weight of the mold. The chain should also be tested and/or replaced on a periodic basis.

To avoid burns from the mold, the company should be tolerate of not pre-heating the mold. Should it be necessary to pre-heat, a heat blanket should be provided to shield the setup person from the hot mold. Warning signs should be mounted on molds that run at extremely high temperatures, as heat blankets are not practical.

As guards are not practical on a scrap grinder, it is necessary to place the dangerous rotating blades far enough away from the opening of the grinder to prevent human contact. Scrap grinders are designed in this way. However, when opening the grinder for maintenance, it becomes possible to reach the blades. To prevent accidents, the grinder should be equipped with an interlock that shuts the blades down when the top is opened. The lockout/tagout program should also apply to grinders.

To avert the issue of plastic flying out of grinders during normal operations, the grinder should be equipped with plastic flaps that the off quality pieces pass by. These flaps would prevent granulated plastic from being expelled from the grinder. In addition, all people operating a grinder should be required to wear safety glasses with side shields or face shields.

Burns that occur due to material dryers can be avoided by adequate insulation. Another improvement that can be made is to limit the length of the hoses. Should a company install material hoppers as suggested above, the length of dryer hose can also be very short. This provides little opportunity for someone to get entangled with the hose.

Three simple fixes are available to elude injuries due to robots trapping a person. Place a fixed guard around the area where the robot operates. This type of guard could be an inconvenience when the robot and/or machine need to be worked on, but it is the most sure way to avoid trapping. A second method involves using safety mats around the area of operation. A safety mat is a device that disables the operation of the robot when sufficient weight (< 10 pounds) is applied to the mat. Thus, when a person walks up to the operational area of the robot, they step on the mat and the robot shuts down. The final method is to create a light curtain around the operational area of the robot. A light curtain operates in the same manner as the safety mats, except that it beams light around the operational area. Then, when one of the light beams are broken, the robot shuts down. All of these methods keep the person away from the robot during its motions.

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IV. Standards

As mentioned in the previous sections on hazard control, there are three standards that directly apply to injection molding machines. These standards are:

  1. ANSI/SPI B151.1: Safety Requirements for the Construction, Care, and Use of Horizontal Injection Molding Machines, Revised 1990.
  2. Recommended Guideline for the Safety Requirements for the Manufacture, Care and Use of Single Station Vertically Clamping Injection Molding Machines. 1992.
  3. Recommended Guideline for the Safety Requirements for the Manufacture, Care and Use of Multiple Station Vertically Clamping Injection Molding Machines. 1996.

All of these standards are comprehensive in nature. They cover the molding machines and all auxiliary equipment, except for robots. Standard (1) & (2) are very similar in nature. There are no discernible differences between the two. The third standard is different in that it adds some clauses related to having multiple stations.

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V. Discussion and Conclusions

The injection molding industry as a whole is becoming safer. Improvements in the standards for injection molding machines have required the machine manufacturers to design safety into their product. John Jarrells, in his interview, discussed what was considered state of the art in years past. When he started in molding (around 1968), the machines were completely open. No guards were around the clamp area, they were considered extraneous and inefficient. Splash guards on the injection unit were also missing. Today, no machine can be sold without these appropriate guards.

Another contributing factor to increased safety is the improvements in material handling systems. In years past, it was not practical to convey the material from silos. It was also believed impractical to mount the hoppers in the floor.

But, in my personal experience, the major improvement in the safety of the injection molding industry has come with a management revolution. In the recent past, injection molding companies were made up of "cowboys," managers that were totally concerned with quantity. Today, as a result of the quality management revolution, managers have a greater respect for the people that work in the industry. As we, the managers, have come to respect our people, we have realized that safety is the most important job in the plant. To give an example of this revolution, I will relate a couple of experiences within the plant that I run.

At Technimark, our material handling system placed people at risk. We still had hoppers mounted on the machines. People climbed ladders to reach platforms to work on the loaders and to clean these hoppers. Fortunately, we have not had an accident, but, the situation offered a tremendous opportunity for an accident. I realized that a major part of my job as Business Unit Manager for this division, I must protect my people at any cost. This year we purchased, at a cost of $500,000, a completely new material handling system that moved the hoppers to the floor. This allows the people to maneuver the loaders and clean the hoppers without climbing on ladders and platforms.

The second situation involves the installation of molds into our molding machines. We increased the size of our molds recently, rendering obsolete the system that we used for installation. The method had become extremely unsafe. We limited the danger by installing the molds in halves. This put not only people at risk, but also the molds. A new, higher capacity fork truck that allows pivoting of the mast (to allow easier maneuvering) was purchased ( $75,000). The new fork truck is rated at greater than twice the weight of our heaviest mold. We also installed a new system to assure that the fork truck and associated equipment (i.e. chains) are tested on a monthly basis.

The injection molding industry is making great strides, but, there are two glaring weaknesses. The first weakness is the general level of training at most companies. The other is enforcement of policies. Many of the 5500 companies are small "mom and pop" type places that do not emphasize safety training or enforcement. As problematic as the "mom and pop" places are, there is also a lack of training and enforcement at some of the larger companies. Upon reviewing the OSHA data for this report, it was discovered that one of the ten largest injection molders in the world had been given a violation (out of 11 violations given to the company) for lockout / tagout.

To ensure that this industry keeps improving its safety record, the managers that have started to see the value in their people must accelerate the pace of improvements. We must not only make the machinery safer, we must force the people themselves to be safer. Gary Clubb, formerly of A&E Products Group, related the story of a person crushed by a molding machine (Clubb interview; OSHA, 14 August 1989). The person that was killed bypassed the electrical and hydraulic interlocks on the machine while working inside of it. All of the needed safety devices were in place, the person was the unsafe factor. With this in mind, we must compel everyone in the industry to understand and fulfill their obligations to safety.

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VI. Reference

American National Standards Institute. ANSI/SPI B151.1: Safety Requirements for the Construction, Care, and Use of Horizontal Injection Molding Machines, Revised 1990. New York: ANSI/SPI, 1990.

Bean, Gary (Technimark Plant Manager). Personal Interview. 12 March 1998.

Clubb, Gary (United Southern Industries Quality Manager). Personal Interview. 14 April 1998.

Griffiths, J.C. "Plastic Injection Injury of the Hand." Injury 8 (1978): 143-144.

Jarrells, John (Technimark VP of Engineering). Personal Interview. 12 March 1998.

Looper, Glenn (Technimark Plant Manager). Personal Interview. 14 March 1998.

National Safety Council. Data Sheet I-454: Injection Molding, Revised 1988. Chicago, IL: Rubber & Plastics Section, 1988.

National Safety Council. Data Sheet I-632: Compression and Transfer Molding of Plastics, Revised 1988. Chicago, IL: Rubber & Plastics Section, 1988.

Nelson, A. "Safety Responsibility in the Plastics Industry." National Safety Congress Transactions 11(1970): 35-36.

Raafat, HMN. "Comparative Strategy for the Safety of Horizontal Injection Moulding Machines." Safety Science 16.1 (1993): 67-88.

Raafat, HMN. "Effectiveness of Standards for the Safety of Horizontal Injection Moulding Machines." Journal of Health and Safety 8(1992): 5-22.

Society of the Plastics Industry. Recommended Guideline for the Safety Requirements for the Manufacture, Care and Use of Single Station Vertically Clamping Injection Molding Machines. Washington, DC: SPI, 1992.

Society of the Plastics Industry. Recommended Guideline for the Safety Requirements for the Manufacture, Care and Use of Multiple Station Vertically Clamping Injection Molding Machines. Washington, DC: SPI, 1996.

State of Wisconsin. Department of Industry, Labor and Human Relations. Analysis of Occupational Injuries and Illnesses for Wisconsin Industry: Miscellaneous Plastics Products. Madison, WI: DILHR Bureau of Research and Statistics, 1976.

United States. Bureau of Labor Statistics. Fatal Occupational Injuries by Industry and Event or Exposure, 1996. Washington, DC: BLS, 1996.

- - -. - - - . Nonfatal Occupational Injury and Illness Incidence Rates per 100 Full Time Workers: 1989. Washington, DC: BLS, 1989.

- - -. - - -. Nonfatal Occupational Injury and Illness Incidence Rates per 100 Full Time Workers: 1990. Washington, DC: BLS, 1990.

- - -. - - -. Nonfatal Occupational Injury and Illness Incidence Rates per 100 Full Time Workers: 1991. Washington, DC: BLS, 1991.

- - -. - - -. Nonfatal Occupational Injury and Illness Incidence Rates per 100 Full Time Workers: 1992. Washington, DC: BLS, 1992.

- - -. - - -. Nonfatal Occupational Injury and Illness Incidence Rates per 100 Full Time Workers: 1993. Washington, DC: BLS, 1993.

- - -. - - -. Nonfatal Occupational Injury and Illness Incidence Rates per 100 Full Time Workers: 1994. Washington, DC: BLS, 1994.

- - -. - - -. Nonfatal Occupational Injury and Illness Incidence Rates per 100 Full Time Workers: 1995. Washington, DC: BLS, 1995.

- - -. - - -. Nonfatal Occupational Injury and Illness Incidence Rates per 100 Full Time Workers: 1996. Washington, DC: BLS, 1996.

- - -. U.S. Department of Labor, Occupational Safety and Health Administration. Establishment Search Inspection Detail, Inspection 003031408 - A&E Products Group, Inc. Washington, DC: OSHA, 14 August 1989.

- - - . - - - . Establishment Search Inspection Detail, Inspection 300079050 - Polar Plastics (Nc) Inc. Washington, DC: OSHA, 18 July 1997.

- - - . - - - . Establishment Search Inspection Detail, Inspection 301828125 - R.A. Serafini, Inc. Washington, DC: OSHA, 28 April 1997.

- - - . - - - . Standards Cited for SIC 3089; All Sizes; Federal. Washington, DC: OSHA, 1997.

- - - . - - - . Standards Cited for SIC 3089; All Sizes; North Carolina. Washington, DC: OSHA, 1997.

- - - . National Institute for Occupational Safety and Health. FACE Report: Injection Mold "Set-Up" Man Electrocuted in Tennessee. Morgantown, WV: NIOSH, 1987.

- - - . - - - . NIOSH Alert: Preventing the Injury of Workers by Robots. Morgantown, WV: NIOSH, 1984.

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