A stripper plate is a plate that strips a molded piece from
core pins or force plugs. The stripper plate is set into operation by the opening of the
mold. The stripper plate mold uses the stripper plate and is similar in some respect
to the loading-shoe mold and the removable-plate mold. It is functionally operated
in the same manner as the loading-shoe mold. The stripper plate fits the core at the
inside of the molded part.
The primary purpose of a stripper plate is to eject the part from the mold without
distorting it or without the presence of objectionable ejector pin marks. The stripper
plate is usually used for parts with thin wall sections (0.010–0.040 in.) when the part cannot be ejected by means of ejector pins. Stripper plate molds are not often
required for thermosetting materials because the finished piece is hard and,
consequently, ejector pins serve satisfactorily for ejection of the parts.
Molding by this method should be confined to units that contain only a small
number of cavities, as temperature differentials may cause binding of the plates.
Conversely, large numbers of cavities would require special attention to minimize
expansion problems.
( Charles A. Harper, Edward M. Petrie, Plastics Materials and Processes: A Concise Encyclopedia, John Wiley & Sons Pub., 2003, p.532-533 )
Differential Scanning Calorimetry (15.04.2011 12:33)
Differential scanning calorimetry is a quality control method that measures the energy absorbed (endotherm) or produced (exotherm) during a specified time and temperature cycle. This technique can be used to determine whether a polymer cures in the same way from batch to batch. It can also be used to show the glass transition temperature of a polymer (generally as a break in the slope of the endothermic curve as a function of temperature).
Differential scanning calorimetry is an alternative to differential thermal analysis
(DTA) for measurement of transition temperatures of polymers, especially where a
determination has a quantitative aspect.
( Charles A. Harper, Edward M. Petrie, Plastics Materials and Processes: A Concise Encyclopedia, John Wiley & Sons Pub., 2003, p.139 )
In-Die Staking (14.04.2011 21:07)
Staking of any hardware is another such operation that could only benefit from automation. Manual staking, similarly to hardware insertion, is cumbersome and slow when done in a separate assembly operation. The inserted hardware is not always large enough for the operator’s fingers to handle, and may often fall down, or be inserted the wrong way, and this way both the sheet-metal part and the hardware may end up in the scrap bin.
In-die staking utilizes a standard bowl feeding equipment as well, along with a customized transfer mechanism. The delivery of parts into the die is done via compressed air. A dual escapement bowl feeder can be used when placing two kinds of hardware at a time. The bowl feeder and its PLC controls are positioned on a portable cart, which allows for mobility from press to press. Designed for a quick change, standardized locators are utilized to attach the portable cart to the press, with quick disconnects for stud insertion and PLC controls. To control the process and to monitor the quality of the parts, sensors are being used in the die. The sensors monitor whether or not
- The material was properly fed
- The studs are present after staking
- The alignment of the studs is correct
- The part is properly ejected
In this case, proximity sensors are implemented to detect the stud presence; photoelectric through beam sensors are there to verify the stock has fed properly. Another photoelectric sensor oversees the parts’ ejection. And all sensors are integrated with the press controls, to prevent any problems during production.
( Ivana Suchy, Handbook of Die Design, McGraw Hill Pub., 2006, Second Edition, p.503-504)
Thermodiffusion Process (About Coating) (14.04.2011 21:25)
Coatings produced by thermodiffusion are formed at high temperatures and in controlled atmospheres of specific content. Diffusing materials of gaseous, solid (powder), or molten form are placed in contact with the part to be coated and allowed to enter its surface. The coated material, usually steel or iron, forms an alloy with the diffusing components within the upper layers of the coated surface. The coating emerges uniform in thickness throughout the part.
The temperature of the process is somewhere near the melting point of the diffused metal and the heating procedure is conducted in an oven. Various processes use different temperature settings: These are either below or above the melting point preferences, according to the diffusion substance used. The temperature of the process influences not only the speed of the coating operation, but also the character and texture of the finish as well.
The most common thermodiffusion processes are cementing and nitriding, but other applications utilizing chromium, aluminum, sulfur, and zinc are being widely used. With zinc, the process is called sheradizing, and the metal material is added in the form of powder. With the melting point of zinc at 786°F, sheradizing is usually performed at temperatures ranging from 600 to 700°F. Thermodiffusing of sulfur is performed along with nitrogen, and the process is almost the same as that of nitriding.
Newer diffusing processes, utilizing boron and silicon, were developed for attainment of an extra high surface hardness, abrasion and wear resistance, and resistance to high temperatures. Another new technique involves a combination of the thermodiffusion process with electrolysis of the salt melt.
Thermodiffusion is preferred as the surface treatment of small parts, since a distortion of products and their dimensional alterations may occur with larger objects. A considerable variation in wall thickness or sharp corners on the part will magnify these complications.
( Ivana Suchy, Handbook of Die Design, McGraw Hill Pub., 2006, Second Edition, p.675-676 )
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