Learn Hardcore Turkish: Demir kapıları boyamadan önce pas temizleme işlemleri yapılmalıdır. - Rust removal procedures must be carried out before painting the iron doors.

The suffix -madan is the negative converb form of a verb plus the ablative case (-ma negative + -dan ablative). It literally means “without doing X,” and when followed by önce it gives “before doing X.”
Formation:
• boya (root “paint”)
• + ma (negative gerund) → boyama (“not painting”)
• + dan (ablative) → boyamadan
So boyamadan önce = “before painting.”

Why is kapıları used instead of just kapılar?

kapılar is “doors” (kapı + -lar plural). We add -ı to make it accusative because the doors are a definite, specific object here (“the iron doors”). So:
kapı + lar (plural) → kapılar
kapılar + ı (accusative) → kapıları

Why does demir stay uninflected while kapı takes plural -lar and case -ı?

In Turkish, adjectives (or nouns used as adjectives) do not take number or case endings—only the head noun does. Here demir (“iron”) describes kapı (“door”), so you pluralize and case-mark kapı:
kapı + lar + ı → kapıları, while demir remains unchanged.

What is temizleme in pas temizleme işlemleri, and how is it formed?