§ 16
How far should the screw convey, and does the form fit the machine?
Answer: Before new mould is set in machine you should know whether shot fits screw. Shot weight is pieces times cavities plus inlet. Screw dispenses melt and melt fills more than finished plastic so shot volume is calculated with melt density eg PP about 0.73-0.75 g/cm³ against 0.905 solid. Dosing distance is shot volume divided by screw cross-section plus mass cushion. Below about 1 × screw diameter melt stands too long in cylinder. Above about 3-4 × diameter melt becomes uneven.
Skudvægt = vægt pr. emne × kaviteter + indløb
Skudvolumen (smelte) = skudvægt ÷ smeltens massefylde
Doseringsvej = skudvolumen × 1000 ÷ (π/4 × snekkediameter²) + massepude (cm³ → mm³)
Rule of thumb: the dosing path should be approximately 1-3 × screw diameter (maximum approximately 4 D). Below 1 D: too long residence time. Over 4 D: uneven melt and air
| Symbol | Meaning | Unit |
|---|---|---|
| emne | Weight per item | g |
| kav | Number of cavities | stk |
| indloeb | Inlet weight per shot (0 for hot runner) | g |
| rho_s | Melt density (datasheet; PP approx. 0.74, ABS approx. 0.95) | g/cm³ |
| snekke | Screw diameter | mm |
| pude | Mass pad | mm |
| = | Dosing path incl. pad | mm |
| = | Dosing path in auger diameters | D |
| = | Shot weight | g |
| = | Shot volume as melt | cm³ |
| = | Inlet's share of the shot | % |
Does not apply when
The calculator's own default values inserted. The figures are calculated with exactly the formula the tool uses.
Substituted
Giver
Members only
Create a free user account to unlock all articles, calculators, templates and range — and get access to quizzes and classes. It takes less than a minute: name, email and a password. No payment card.
Want to try something first? See what you can use without an account — the junior zone, the encyclopedia, the videos and more.
Når en form skal flyttes til en anden maskine, eller en ny form skal køres ind, skal du vide, om skuddet passer til snekken. Doseringsvejen viser, hvor langt snekken skal trække tilbage for at dosere skuddet. Den bruges sammen med lukkekraften til at vælge den rigtige maskine.
En 4-kavitetsform til låg på 25 g med et 8 g indløb skal køre i PP på en maskine med 35 mm snekke.
It means: Doseringsvejen bliver 157 mm, altså 4.5 D. Det er for langt til snekken, så smelten bliver ujævn. Flyt formen til en maskine med større snekke.
Du prøver formen på en maskine med 45 mm snekke.
It means: Nu er doseringsvejen 97 mm, eller 2.2 D. Det ligger fint inden for 1-3 D. Skudvægten er 108 g.
En 8-kavitetsform til små knapper på 3 g i ABS med 2 g indløb skal køre på en 25 mm snekke.
It means: Doseringsvejen er 61 mm, svarende til 2.4 D. Indløbet er 7.7 % af skuddet.
Doseringsvej ca. 1-3 × snekkediameteren. Over ca. 4 D er snekken for lille.
Skudvolumen ÷ snekkens tværsnit skal give doseringsvejen uden pude. 146 cm³ ÷ 9,62 cm² ≈ 15 cm.